Aqueous dispersions containing polymerizates produced in multiple stages and coating agent compositions containing same

ABSTRACT

Described herein are aqueous dispersions including multistage-prepared polymers of olefinically unsaturated compounds and to the preparation and use thereof, in particular in the field of automobile coating.

The present invention relates to aqueous dispersions comprisingmultistage-prepared polymers of olefincally unsaturated compounds, andalso to their preparation and use, especially within the field ofautomotive finishing.

PRIOR ART

Known from the prior art are polymers which can be used as binders forautomotive finishing. A binder of this kind is required to fulfill amultiplicity of properties. It must, for instance, be capable of beingused in modern multicoat paint systems of the kind employed is theautomobile industry.

The prior art (cf., e.g., German. patent application DE 199 48 004 A1,page 17, line 37 to page 19, line 22, or German patent DC 100 43 405 C1,column 3, paragraph [0018], and column 8, paragraph [0052] to column 9,paragraph [0057] , in conjunction with column 6, paragraph [0039] tocolumn 8, paragraph [0050]) has disclosed the following process, inwhich

-   (1) a pigmented aqueous basecoat material is applied to a substrate,-   (2) a polymer film is formed from the coating material applied in    stage (1),-   (3) a clearcoat material is applied to the resulting basecoat film,    and subsequently-   (4) the basecoat film is cured together with the clearcoat film,    to give a multi coat paint system.

This process is widely employed, for example, not only for the OEM(original) finishing of automobiles but also for the painting ofancillary components made from metal and plastic.

The resulting multicoat paint system is required to fulfill amultiplicity of properties.

Where coating defects occur, the vehicle bodies are coated a second timewith the basecoat and clearcoat materials by the aforementioned process.In this coating procedure, in OEM automotive refinishing, the coatingmaterial used may be the same as for the first coating. Also possible,however, is the use of a clearcoat material which cures not at hightemperatures (around. 140° C.) but instead, at much lower temperatures(about 80° C.) The resultant paint system must meet the high demands ofthe automobile industry for appearance and stability; the adhesionbetween the original finish and the basecoat material used in therefinishing operation may present particular difficulties.

A polymer which has been known in the prior art for many years, andwhich even now has retained high relevance as a binder in automotive OEMfinishing, is a polyurethane which is known from WO 92/15405. Thisbinder is used with the aim of improving the refinish adhesion, and cantherefore serve as a reference for adhesion properties.

In Korea Polymer Journal (Korea Polym. J., vol. 7 no. 4, pp. 213-222)Hong, Kim, Kim and Park describe polymers of multistage construction foruse as binders in metallic finishes. These polymers are produced via anoperation in which the first stage of the polymer is prepared by a batchoperation and the second and third stages are each carried out asstarved feed polymerizations.

Problem

The problem addressed with the present invention, then, was that ofproviding a polymer which can be used to produce coatings which resolvethe difficulties described above.

By this is meant an improved adhesion both for the painting of metallicand plastics substrates and also, in particular, for automotiverefinish, for the case both of OEM clearcoat materials with a bakingtemperature of generally about 140° C. and of refinish clearcoatmaterials with a baking temperature of in general about 80° C. In thecontext of improving adhesion, the focus is on the improved adhesionbetween basecoat and original finish. It is this adhesion which is to beimproved in particular for use in OEM automotive refinishing.

The adhesion difficulties are especially striking when the coatedsubstrates are exposed to weathering. The problem addressed by thepresent invention was therefore also that of providing a polymer forcoatings which possess outstanding adhesion properties even after havingbeen exposed to weathering.

Weathering is often a precursor of other difficulties, especiallyblisters and swelling. A further problem addressed by the presentinvention, therefore, was that of preventing or reducing incidence ofblisters and swelling.

In addition to the adhesion improvements described, the problemaddressed by the present invention was that of providing polymers whichwhen used in coating materials display improved properties in termsstorage stability of the coating materials, as compared with the priorart.

Another problem addressed by the present invention was that of providinga polymer which when used in coating materials fulfills the requirementsof automotive OEM finishing in terms of target flop in the case ofeffect finishes, in terms of sufficiently high solids for obtainingsufficiently high film thicknesses, and in terms of a viscosity whichpermits processing by means of electrostatic and/or pneumaticapplication.

Solution to the problem

It has emerged that the problems described above can be solved by anaqueous dispersion comprising at least one polymer and preparable by

-   -   i. polymerizing a mixture olefincally unsaturated monomers A by        emulsion polymerization in water, using at least one emulsifier        and at least one water-soluble initiator, where a polymer        prepared from the monomers A has a glass transition temperature        of 10 to 55° C.    -   ii. polymerizing a mixture of olefinically unsaturated monomers        B by emulsion polymerization in water, using at least one        emulsifier and at least one water-soluble initiator, in the        presence of the polymer obtained under i., where a monomers        concentration of 6.0 wt % in the reaction solution is not        exceeded throughout the reaction period, and        -   the mixture of olefinically unsaturated monomers B comprises            at least one polyolefinically unsaturated monomer,    -   iii. polymerizing a mixture of olefinically unsaturated monomers        C by emulsion polymerization in water, using at least one        emulsifier and at least one water-soluble initiator, in the        presence of the polymer obtained under ii., where a monomers        concentration of 6.0 wt % in the reaction solution is not        exceeded throughout the reaction period, and    -   iv. adjusting the pH of the reaction solution to a pH of 6.5 to        9.0,        -   wherein        -   a. the mixture olefinically unsaturated monomers A comprises            from 0 wt % to less than 50.0 wt % of one or more monomers            having a solubility in water of <0.5 g/l at 25° C.,            -   a monomers A concentration of 6.0 wt % in the reaction                solution from stage i. is not exceeded,            -   and the resulting polymer after stage i. has a particle                size of 20 to 110 nm,        -   b. a polymer prepared from the monomers B has a glass            transition temperature of −35 to 12° C., and            -   the resulting polymer after stage ii. has a particle                size of 130 to 200 nm,        -   c. a polymer prepared from the monomers C has a glass            transition temperature of −50 to 15° C., and            -   the resulting polymer after stage iii. has a particle                size of 150 to 280 nm.

The new aqueous dispersion comprising at least one polymer is alsoreferred to below as aqueous dispersion of the invention. Preferredembodiments of the aqueous dispersion of the invention are apparent fromthe description which follows and also from the dependent claims.

The above-described polymer is a so-called seed-core-shell polymer andis also referred to as seed-core-shell acrylate in the presentapplication.

Likewise provided by the present invention is a pigmented aqueousbasecoat material comprising the aqueous dispersion of the invention asbinder, and also the use of the aqueous dispersion of the invention inaqueous basecoat materials for improving adhesion. The present inventionrelates not least to a process for producing a multicoat paint system ona substrate, and also to a multicoat paint system produced by the statedprocess. The present invention also relates to a method for repairingdefect sites in multicoat paint systems, using the basecoat material ofthe invention.

The term “comprising” in the sense of the present invention, inconnection with the aqueous dispersion of the invention, has in onepreferred embodiment the meaning of “consisting of”. The term“comprising” in the sense of the present invention, in connection withthe aqueous basecoat material, has in one preferred embodiment themeaning of “consisting of”. With regard to the aqueous basecoatmaterials of the invention in this preferred embodiment, one or more ofthe components identified later on below and present optionally in theaqueous basecoat material of the invention may be present in the aqueousbasecoat material. All components may each be present in theirbelow-stated preferred embodiments in the aqueous basecoat material ofthe invention.

With regard to the aqueous dispersions, a dispersion is named aqueouswhen it comprises a significant fraction of water. In this context,within the present invention “aqueous” is preferably to be understood tomean that the dispersion has a water fraction of at least 40 wt %,preferably at least 50 wt %, very preferably at least 60 wt %, based ineach. case on the total amount of the solvents present (that is, waterand organic solvents). With particular preference the water fraction is40 to 99 wt %, more particularly 50 to 98 wt %, very preferably 60 to 95wt %, based in each case on the total amount of the solvents present.

The term “(meth)acrylate” is intended below to denote both acrylate andmethacrylate.

For standards, as for example DIN standards, for which no version or noyear of issue is explicitly stated, the valid version is that which wasvalid on the filing date or, if there was no valid version in existenceon the filing date, then the last valid version of the standard.

The aqueous dispersion

The aqueous dispersions of the invention are prepared by multistageradical emulsion polymerization of olefinically unsaturated monomers inwater.

The radical emulsion polymerization requires at least one polymerizationinitiator. The polymerization initiator used must be a water-solubleinitiator. Preference is given to using an initiator selected from theof potassium, sodium, or ammonium peroxodisulfate, hydrogen peroxide,tert-butyl hydroperoxide, 2,2′-azobis(2-amidoisopropane)dihydrochloride, 2,2′-azo-bis(N,N′-dimethylene-isobutyramidine)dihydrochloride, 2,2′-azobis(4-cyanopentanoic acid), or mixtures of theaforementioned initiators, e.g., hydrogen peroxide and sodiumpersulfate, and to redox initiator systems.

For all stages i), ii), and iii) of the emulsion polymerizations, atleast one polymerization initiator required in each case. The at leastone polymerization initiator in each of stages i), ii) and iii) of theemulsion polymerization is selected independently of the polymerizationinitiators of the other stages. With preference the same polymerizationinitiator is used in each of stages i), ii) and iii) of the emulsionpolymerization.

Redox initiator systems are those initiators which comprise at least oneperoxide-containing compound in combination with a redox coinitiator,examples being sulfur compounds with a reductive activity, as forexample bisuifites, sulfites, thiosulfates, dithionites, ortetrathionates of alkali metals and ammonium compounds, sodiumhydroxymethanesulfinate dihydrate and/or thiourea. Accordingly,combinations of peroxodisulfates with alkali metal or ammoniumhydrogensulfites can be used, e.g., ammonium peroxodisulfate andammonium disulfite. The weight ratio of peroxide-containing compounds tothe redox coinitiators is preferably 50:1 to 0.05:1. In combination withthe initiators or with the redox initiator systems, it is possibleadditionally to employ transition metal catalysts, such as iron, nickel,cobalt, manganese, copper, vanadium, or chromium salts, for example,such as iron(II) sulfate, cobalt(II) chloride, nickel(II) sulfate,copper(I) chloride, manganese(II) acetate, vanadium(III) acetate, andmanganese(II) chloride. Relative to the monomers, these transition metalsalts are used customarily in amounts of 0.1 to 1000 ppm. Accordingly,combinations of hydrogen peroxide with iron (II) salts can be used, suchas 0.5 to 30% hydrogen peroxide and 0.1 to 500 ppm Mohr's salt, forexample.

The initiators are used preferably in an amount of 0.05 to 20 wt %,preferably 0.05 to 10, more preferably of 0.1 to 5 wt %, based on thetotal weight of the monomers used in the respective stage.

The polymerization is carried out usefully at a temperature of 0 to 160°C., preferably of 60 to 95° C.

It is preferred here to operate in the absence of oxygen, preferablyunder an inert gas atmosphere. Generally speaking, the polymerization iscarried out under atmospheric pressure, although the use of lowerpressures or higher pressures is also possible, especially ifpolymerization temperatures are employed which lie above the boilingpoint of the monomers and/or solvents.

Individual stages of the multistage emulsion polymerization forproducing the aqueous dispersions of the invention must be carried outas a so-called “starved feed” polymerization (also known as “starvefeed” or “starve fed” polymerization).

Starved feed polymerization in the sense of the present invention isconsidered an emulsion polymerization wherein the amount of residualmonomers in the reaction solution is minimized throughout the reactionperiod—that is, the metered addition of the olefinically unsaturatedmonomers takes place in such a way that a concentration of 6.0 wt %,preferably 5.0 wt %, more preferably 4.0 wt %, very advantageously 3.5wt %, in the reaction solution is not exceeded throughout the reactionperiod. Even more preferred are concentration ranges for theolefinically unsaturated monomers of 0.0 to 6.0 wt %, preferably 0.02 to5.0 wt %, and more preferably 0.03 to 4.0 wt %, more particularly 0.05to 3.5 wt %. For example, the highest fraction (or the concentration)detectable during the reaction may be 0.5 wt %, 1.0 wt %, 1.5 wt %, 2.0wt %, 2.5 wt %, or 3.0 wt %, while all other detected values then liebelow the values specified here.

The concentration of the monomers in the reaction solution may bedetermined here, for example, by gas chromatography:

after sampling, the sample is immediately cooled with liquid nitrogenand admixed with 4-methoxyphenol as inhibitor. In the next step, thesample is dissolved in tetrahydxofuran and n-pentane is added. The clearsupernatant is analyzed by gas chromatography, using a polar column andan apolar column for determining the monomers, and a flame ionizationdetector. Typical parameters for the gas-chromatographic determinationare as follows: 25 m silica capillary column with 5% phenyl-, 1%vinyl-methylpolysiloxane phase, or 30 m silica capililary column with50% phenyl- and 50% methyl-polysiloxane phase, hydrogen carrier gas,150° C. split injector, oven temperature 50 to 180° C., flame ionizationdetector, detector temperature 275° C., internal standard isobutylacrylate.

For the purposes of the present invention, the monomer concentration isdetermined preferably by gas chromatography, more particularly withcompliance with the parameters stated above.

The concentration of the monomers in the reaction solution, referred tobelow as free monomers, may be controlled in a variety of ways.

One possibility for minimizing the concentration of the free monomers isto select a very low metering rate for the mixture of olefinicallyunsaturated monomers. If the metering rate is low enough to allow all ofthe monomers to react extremely quickly as soon as they are in thereaction solution, it is possible to ensure that the concentration ofthe free monomers is minimized.

In addition to the metering rate, it is important that the reactionsolution always contains sufficient radicals to allow the monomersmetered in to be reacted extremely quickly, hence guaranteeing furtherchain growth and minimizing the concentration of free monomer.

For this purpose, the reaction conditions should preferably be selectedsuch that initiator feed is commenced even before the start of themetering of the olefinically unsaturated monomers.

The metered addition is preferably commenced at least 5 minutes before,more preferably at least 10 minutes before. With preference at least 10wt % of the initiator, more preferably at least 20 wt %, very preferablyat least 30 wt % of the initiator, based in each case on the totalamount of initiator, is added before the start of the metering of theolefinically unsaturated monomers.

The temperature selected should be one which allows constantdecomposition of the initiator.

The amount of initiator is an important factor for the sufficientpresence of radicals in the reaction solution. The amount of initiatorshould be selected such that sufficient radicals are available at anytime, allowing the monomers metered in to react. If the amount ofinitiator is increased, it is also possible for larger amounts ofmonomers to be reacted at the same time.

Another factor determining the reaction rate is the reactivity of themonomers.

Controlling the concentration of the free monomers can therefore beaccomplished by the interplay of initiator amount, rate of initiatoraddition, rate of monomer addition, and selection of the monomers. Notonly the slowing of metering, but also the raising of initiator amount,and also the early commencement of initiator addition, serve the aim ofkeeping the concentration of the free monomers within the limits statedabove.

At any juncture in the reaction, the concentration of the free monomerscan be determined by gas chromatography, as described above.

Should this analysis find a concentration of free monomers which isclose to the limit value for the starved feed polymerization, on accountof olefinically unsaturated monomers having a very low reactivity, forexample, the parameters stated above may be utilized for the control ofthe reaction. In this case, for example, the monomer metering rate canbe reduced, or the amount of initiator can be increased.

Via the controlled conditions of starved feed polymerization, precisecontrol is possible over the morphology and particle size of theresulting polymer, by the metered addition of the monomers being stoppedwhen particle size has been achieved.

In this context, a sample of the reaction solution can be taken at anytime, and the particle size determined by means of dynamic lightscattering in accordance with DIN ISO 13321.

All stages i), ii), and iii) of the emulsion polymerization require ineach case at least one emulsifier. The at least one emulsifier in eachof stages i), ii), and iii) of the emulsion polymerization is selectedindependently of the emulsifiers of the other stages. With preferencethe same emulsifier is used in each of stages i), ii), and iii) of theemulsion polymerization.

The emulsifiers are used preferably in an amount of 0.1-10.0 wt %, morepreferably 0.1-5.0 wt %, very preferably 0.1-3.0 wt %, based in eachcase on the total weight of the monomers in the respective stage.

Nonionic or ionic emulsifiers, and zwitterionic emulsifiers as well, andalso, optionally, mixtures of the aforementioned emulsifiers, can beused.

Preferred emulsifiers are optionally ethoxylate or propoxylated alkanolshaving 10 to 40 carbon atoms and having different degrees ofethoxylation and/or propoxylation (e.g., adducts with 0 to 50 mol ofalkylene oxide), and/or their neutralized, sulfated, sulfonated orphosphated derivatives.

Particularly preferred emulsifiers are neutralized dialkylsulfosuccinicesters or alkyldiphenyl oxide disulfonates, available commercially forexample as EF-800 from Cytec.

For the purposes of the invention, the glass transition temperature Tgis determined experimentally on the basis of DIN 51005 “Thermal analysis(TA)—terms” and DIN 53765 “Thermal analysis—differential scanningcalorimetry (DSC)”. This involves weighing out a 10 mg sample into asample boat and introducing it into a DSC instrument. The instrument iscooled to the start temperature, after which 1^(st) and 2^(nd)measurement runs are carried out under inert gas flushing (i2) at 50mi/min, with a heating rate of 10 K/min, with cooling to the starttemperature again between the measurement runs. Measurement takes placecustomarily in the temperature range from about 50° C. lower than theexpected glass transition temperature to about 50° C. higher than theglass transition temperature. The glass transition temperature for thepurposes of the present invention, in accordance with DIN 53765, section8.1, is the temperature in the 2nd measurement run at which half of thechange in the specific heat capacity (0.5 delta cp) is reached. Thistemperature is determined from the DSC diagram (plot of the thermal flowagainst the temperature), and is the temperature at the point ofintersection of the midline between the extrapolated baselines, beforeand after the glass transition, with the measurement plot.

All of the values reported below for glass transition temperatures Tgrelate to the particular polymer which is formed when the respectivemonomer mixture polymerized individually. The value obtained for thethird stage, for example, is therefore the value obtained when themonomer mixture of the third stage is polymerized in the absence of thefirst and second stages.

For a purposive estimation of the anticipated glass transitiontemperatures, the equation known as the Fox equation can be used:

Fox equation:

$\frac{1}{T_{g}} = {\frac{x_{1}}{T_{g\; 1}} + \frac{x_{2}}{T_{g\; 2}} + \ldots + \frac{x_{n}}{T_{gn}}}$

Tg: glass transition temperature of the resulting copolymer (kelvins)

x₁, x₂, . . . , x_(n): Weight portion of the monomer component 1, 2, . .. , n

T_(g1) T_(g2), . . . , T_(gn): glass transition temperature of thehomopolymer of the monomer component 1, 2, . . . , n (kelvins).

Since the Fox equation represents only an approximation, based on theglass transition temperatures of the homopolymers and their weightportions, without including a molecular weight, it can be used only as atool or a purposive indicator to the skilled person in the synthesis.

The only glass transition temperature values relevant for thedescription of the present invention are those measured as describedabove.

All of the acid numbers and hydroxyl numbers reported below are valuescalculated on the basis of the monomer compositions.

Suitable olefinically unsaturated monomers may be mono- orpolyolefinically unsaturated.

Examples of suitable monoolefinically unsaturated monomers include(meth)acrylate-based monoolefinically unsaturated monomers, vinylicmonoolefinically unsaturated monomers, alpha-beta unsaturated carboxylicacids, and allyl compounds.

The (meth)acrylate-based monoolefinically unsaturated monomers may be,for example, (meth)acrylic acid and esters, nitriles, or amides of(meth)acrylic acid.

Preference is given to esters of (meth)acrylic acid having a raedical Rwhich is not olefinically unsaturated.

The radical R may be aliphatic or aromatic. The radical R is preferablyaliphatic. The radical R may be, for example, an alkyl radical, or maycontain heteroatoms.

Examples of radicals R which contain heteroatoms are ethers. Preferenceis given to using at least, but not necessarily exclusively, monomers inwhich the radical R is an alkyl radical.

If R is an alkyl radical, it may be a linear, branched, or cyclic alkylradical. In all three cases, the radicals in question may beunsubstituted or else substituted by functional groups. The alkylradical preferably has 1 to 20, more preferably 1 to 10, carbon atoms.

Monounsaturated esters of (meth)acrylic acid with an unsubstituted alkylradical that are suitable with particular preference are methyl(meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl(meth)acrylate, n-butyl (meth) acrylate, isobutyl (meth) acrylate,test-butyl (meth) acrylate, amyl (meth) acrylate, hexyl (meth)acrylate,ethylhexyl (meth) acrylate, 3,3,5-trimethylhexyl (meth) acrylate,stearyl (meth) acrylate, lauryl (meth) acrylate, cycloalkyl(meth)acrylates, such as cyclopentyl (meth) acrylate, isobornyl(meth)acrylate, and also cyclohexyl (meth) acrylate, with n- andtest-butyl (meth)acrylate and methyl methacrylate being especiallypreferred.

Suitable monounsaturated esters of (meth)acrylic acid with a substitutedalkyl radical may be substituted preferably by one or more hydroxylgroups or by phosphoric ester groups.

Monounsaturated esters of (meth)acrylic acid with an alkyl radicalsubstituted by one or more hydroxyl groups, suitable with particularpreference, are 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl(meth)acrylate, 3-hydroaypropyl (meth)acrylate, hydroxybutyl(meth)acrylate and 4-hydroxybutyl (meth)acrylate, with 2-hydroxyethyl(meth)acrylate being especially preferred.

Monounsaturated esters of (meth)acrylic acid with phosphoric estergroups, of particularly preferred suitability, are, for example, thephosphoric ester of polypropylene glycol monomethacrylate, such as thecommercially available Sipomer PAM 200 from Rhodia.

The vinylic monounsaturated monomers may be monomers having a radical R′on the vinyl group that is not olefinically unsaturated.

The radical R′ may be aliphatic aromatic, with aromatic radicals beingpreferred.

The radical R′ may be a hydrocarbon radical or may contain heteroatoms.Examples of radicals R′ which contain heteroatoms are ethers, esters,amides, nitriles, and heterocycles. The radical R′ is preferably ahydrocarbon radical. Where R′ is a hydrocarbon radical, it may beunsubstituted or substituted by heteroatoms, with unsubstituted radicalsbeing preferred. The radical R′ is preferably an aromatic hydrocarbonradical.

Particularly preferred vinylic olefinically unsaturated monomers arevinylaromatic hydrocarbons, especially vinyltoluene,alpha-methylstyrene, and especially styrene.

If heteroatoms are included, olefinically unsaturated monomers arepreferred, such as acrylonitrile, methacrylonitrile, acrylamide,methacrylamide, N-dimethylacrylamide, vinyl acetate, vinyl propionate,vinyl chloride, N-vinylpyrrolidone, N-vinylcaprolactam,N-vinylformamide, N-vinylimidazole, and N-vinyl-2-methylimidazoline.

The radical R′ may preferably have the following structure:

In this structure, the radicals R1 and R2 are alkyl radicals having atotal of 7 carbon atoms. Monomers of this kind are availablecommercially under the name VEOVA 10 from Momentive.

Examples of suitable polyolefinically unsaturated monomers encompassesters of (meth)acrylic acid with an olefinically unsaturated radicalR″, and allyl ethers of mono- or polyhydric alcohols. The radical R″ maybe an allyl radical or a (meth)acryloyl radical.

Preferred polyolefinically unsaturated monomers include ethylene glycoldi(meth)acrylate, 1,2-propylene glycol di(meth)acrylate, 2,2-propyleneglycol di(meth)acrylate, butane-1,4-diol di(meth)acrylate, neopentylglycol di(meth)acrylate, 3-methylpentanediol di(meth)acrylate,diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate,tetraethylene glycol di(meth)acrylate, dipropylene glycoldi(meth)acrylate, tripropylene glycol di(meth)acrylate, hexanedioldi(meth)acrylate, and allyl (meth) acrylate.

Preferred polyolefinically unsaturated compounds additionally includeacrylic and methacrylic esters of alcohols having more than two OHgroups, such as, for example, trimethylolpropane tri(meth)acrylate orglycerol tri(meth)acrylate, but also trimethylolpropane di(meth)acrylatemonoallyl ether, trimethylolpropane (meth)acrylate diallyl ether,pentaerythritol tri(meth)acrylate monoallyl ether, pentaerythritoldi(meth)acrylate diallyl ether, pentaerythritol (meth)acrylate triallylether, triallylsucrose, and pentaallylsucrose.

Particular preference is given to using hexanediol di(meth)acrylateand/or allyl methacrylate, very preferably a combination of hexanedioldi(meth)acrylate and allyl methacrylate.

The solubility of the organic monomers in water can be determined viaestablishment of equilibrium with the gas space above the aqueous phase(in analogy to the reference X.-S. Chai, Q. X. Hou, F. J. Schott,Journal of Applied Polymer Science vol. 99, 1296-1301 (2006)).

For this purpose, in a 20 ml gas space sample tube, to a defined volumeof water, preferably 2 ml, an excess in relation to the solubility ofthe monomer to be determined, and an addition of 10 ppm of an emulsifierare added. In order to obtain the equilibrium concentration, the mixtureis shaken continually. The supernatant gas phase is replaced by an inertgas, thus re-establishing an equilibrium. In the gas phase removed, thefraction of the substance to be detected is measured (preferably bymeans gas chromatography). The equilibrium concentration in water can bedetermined by plotting the fraction of the monomer in the gas phase as agraph. The slope of the curve changes from a virtually constant value(S1) to a significantly negative slope (S2) as soon as the excessmonomer fraction has been removed from the mixture. The equilibriumconcentration here is reached at the point of intersection of thestraight line with the slope S1 and of the straight line with the slopeS2.

The determination described is carried out preferably at 25° C.

Stage i. of preparing the aqueous dispersions of the invention is thereaction of a mixture of olefinically unsaturated monomers A by emulsionpolymerization in water, using at least one emulsifier and at least onewater-soluble initiator, with the mixture of olefinically unsaturatedmonomers A being metered in such that the monomers concentration in thereaction solution does not exceed 6.0 wt %, preferably 5.0 wt %, morepreferably 4.0 wt % throughout the reaction period, in other words suchas to observe the reaction conditions for a starved feed polymerization.

The resulting polymer from stage i, is referred to below as seed.

The total mass of the monomer mixture A here preferably has a fractionof 1.0 to 10.0%, more preferably 2.0 to 6.0%, based on the total mass ofthe monomer mixtures A, B, and C.

The mixture of olefincally unsaturated monomers A here is selected suchthat the resulting polymer has a glass transition temperature Tg of 10to 55° C., preferably of 30 to 50° C.

The mixture of olefinically unsaturated monomers A comprises from 0 wt%, preferably from 10 wt %, more preferably from 25 wt %, and verypreferably from 35 wt % to less than 50.0 wt %, preferably less than49.0 wt %, more preferably less than 48.0 wt %, and very preferably lessthan 45.0 wt %, based on the total mass of the mixture of olefinicallyunsaturated monomers A, of one or more monomers having a solubility inwater at a temperature of 25° C. of <0.5 g/l.

The monomers having a solubility in water at a temperature of 25° C. of<0.5 g/l preferably comprise styrene.

The reaction conditions for the polymerization are selected such thatthe resulting polymer after stage i. has a particle size of 20 to 110nm.

The monomer mixture A preferably contains no hydroxy-functionalmonomers.

The monomer mixture A preferably contains no acid-functional monomers.

The monomer mixture A more preferably comprises at least onemonounsaturated ester of (meth)acrylic acid having an unsubstitutedalkyl radical, and/or at least one vinylic monounsaturated monomerhaving an aromatic radical on the vinyl group. The monounsaturated esterof the (meth)acrylic acid having an unsubstituted alkyl radical ispreferably n-butyl acrylate or ethyl acrylate. The vinylicmono-unsaturated monomer having an aromatic radical on the vinyl groupis preferably styrene.

Stage ii. of preparing the aqueous dispersions of the invention is thereaction of a mixture of olefinically unsaturated monomers B by emulsionpolymerization in water, using at least one emulsifier and at least onewater-soluble initiator, in the presence of the polymer obtained underi., the seed, with the mixture of olefinically unsaturated monomers Bbeing metered in such that a monomers concentration of 6.0 wt %,preferably 5.0 wt %, more preferably 4.0 wt % in the reaction solutionis not exceeded throughout the reaction period, thereby observing thereaction conditions for a starved feed polymerization.

The polymer resulting from the mixture of olefinically unsaturatedmonomers B is referred to below as core. The overall outcome, in otherwords the resulting polymer after stage (ii.), is therefore acombination of seed and core.

The total mass of the monomer mixture B here preferably has a fractionof 60 to 80%, more preferably 70 to 80%, very preferably of 71 to 77%,based on the total mass of the monomer mixtures A, B, and C.

The mixture of olefinically unsaturated monomers B here selected suchthat a polymer prepared from the monomers B has a glass transitiontemperature Tg of −35 to +12° C., preferably of −25 to −7° C.

The reaction conditions for the polymerization are selected such thatthe resulting polymer after stage ii., i.e., seed and core, has aparticle size of 130 to 200 nm

The monomer mixture B comprises at least one polyolefinicallyunsaturated monomer.

The monomer mixture B preferably contains no acid-functional monomers.

The monomer mixture B preferably contains no hydroxy-functionalmonomers.

The monomer mixture B preferably comprises at least one polyolefinicallyunsaturated monomer and at least one monounsaturated ester of(meth)acrylic acid having an unsubstituted alkyl radical. In oneespecially preferred embodiment the monomer mixture B additionallycomprises at least one vinylic monounsaturated monomer having anaromatic radical on the vinyl group.

Stage iii. of preparing the aqueous dispersions of the invention is thereaction of a mixture of olefinically unsaturated monomers C by emulsionpolymerization in water, using at least one emulsifier and at least onewater-soluble initiator, in the presence of the polymer obtained underii., consisting of seed and core, with the mixture of olefinicallyunsaturated monomers being metered in such that a monomers concentrationof 6.0 wt %, preferably 5.0 wt %, more preferably 4.0 wt % in thereaction solution is not exceeded throughout the reaction period,thereby observing the reaction conditions for a starved feedpolymerization.

The polymer resulting from the mixture of olefinically unsaturatedmonomers C is referred to below as shell. The overall outcome, in otherwords the resulting polymer after stage (ii.), is therefore acombination of seed, core, and shell. The overall multistage polymer isalso identified as a seed-core-shell polymer.

The total mass of the monomer mixture C here has a fraction ofpreferably 10 to 30%, more preferably of 18 to 24%, based on the totalmass of the monomer mixtures A, B, and C.

The mixture of olefinically unsaturated monomers C is selected here suchthat a polymer prepared from the monomers C has a glass transitiontemperature Tg of −50 to 15° C., preferably of −20 to −12° C.

The mixture of olefinically unsaturated monomers C is preferablyselected here such that the resulting polymer, consisting of seed, core,and shell, has an acid number of 10 to 25.

Preferably the monomers for the mixture of olefinically unsaturatedmonomers C are selected here such that the resulting polymer, consistingof seed, core, and shell, has an OH number of 0 to 30, more preferablyof 10 to 25.

The reaction conditions for the polymerization are selected such thatthe resulting polymer after stage iii. has a particle size of 150 to 280nm.

The monomer mixture C preferably comprises at least one alpha-betaunsaturated carboxylic acid.

In one particularly preferred embodiment the monomer mixture C comprisesat least one alpha-beta unsaturated carboxylic acid and at least onemonounsaturated ester of (meth)acrylic acid having an alkyl radicalsubstituted by one or more hydroxyl groups.

In one especially preferred embodiment the monomer mixture C comprisesat least one alpha-beta unsaturated carboxylic acid, at least onemonounsaturated ester of (meth)acrylic acid having an alkyl radicalsubstituted by one or more hydroxyl groups and at least onemonounsaturated ester of (meth)acrylic acid having an unsubstitutedalkyl radical.

In one preferred embodiment the mass of the monomer mixture A, based onthe total mass of the monomer mixtures A, B, and C, is 1 to 10%, themass of the monomer mixture B, based on the total mass of the monomermixtures A, B, and C, is 60 to 80%, and the mass of the monomer mixtureC, based on the total mass of the monomer mixtures A, B, and C, is 10 to30%.

In one particularly preferred embodiment the mass of the monomer mixtureA, based on the total mass of the monomer mixtures A, B, and C, is 2 to6%, the mass of the monomer mixture B, based on the total mass of themonomer mixtures A, B, and C, is 71 to 77%, and the mass of the monomermixture C, based on the total mass of the monomer mixtures A, B, and C,is 18 to 24%.

Stage iv. of preparing the aqueous polymer dispersions of the inventionis the neutralization of the reaction solution. By neutralization ismeant adjustment to a pH of 6.5 to 9.0 by addition of a base, preferablyby addition of an amine. Employed with particular preference for theneutralization is N,N-dimethyl-ethanolamine (DMEA).

The measurement of the pH here carried out preferably using a pH meter(for example, Mettler-Toledo S20 SevenEasy pH Meter) having a combinedpH electrode (for example, Mettler-Toledo Intab® Routine).

The polymers after neutralization preferably have a particle size(z-average) of 100 to 400, more preferably of 220 to 330 nm.

The OH number of the polymers is preferably between 0 and 200 mg/g KOH.

The solids content, or solids, refers to the weight fraction remainingas a residue on evaporation under specified conditions. The solidscontent of the aqueous dispersion of the invention is determined inaccordance with DIN EN ISO 3251 at 125° C., 60 minutes, initial mass 1.0g (table A.2, Method C of DIN EN ISO 3251).

The gel fraction of the aqueous dispersion of the invention preferablyat least 70 wt %, more preferably at least 80 wt %, based in each caseon the solids content of the dispersion.

Gel fraction can determined gravimetrically by centrifuging thedispersion. This is done by diluting the dispersion with tetrahydrofuranand using an ultracentrifuge to remove the insoluble fraction. The driedinsoluble fraction is subsequently weighed, and the ratio is formed withthe total solids content of the dispersion. The value obtainedcorresponds to the gel fraction.

The pigmented Aqueous Basecoat Material

The present invention further relates to a pigmented aqueous basecoatmaterial which comprises at least one aqueous dispersion of theinvention.

A basecoat material is an intermediate, color-imparting coating materialwhich is used in automotive finishing and general industrial coating. Itis generally applied to a metallic or plastic substrate that has beenpretreated with surfacer or with primer-surfacer, or else occasionallydirectly to the plastics substrate. Serving as substrates may also beexisting paint systems, which optionally must also be pretreated (bybeing abraded, for example). In order to protect a basecoat film againstenvironmental influences in particular, at least an additional clearcoatfilm is applied over it.

The weight percentage fraction of the at least one aqueous dispersion ofthe invention, based on the total weight of the aqueous basecoatmaterial, is preferably 5.0 to 60.0 wt %, more preferably 10.0 to 50.0wt %, and very preferably 20.0 to 45.0 wt %.

The weight percentage fraction or the polymers originating from theaqueous dispersions of the invention, based on the total weight of theaqueous basecoat material, is preferably 1.0 to 24.0 T %, preferably 2.5to 20.0 wt %, and more preferably 3.0 to 18.0 wt %.

In the case of a possible particularization to basecoat materialscomprising preferred components in a specific fractional range, thefollowing applies: the components which do not fall within the preferredgroup may of course still be present in the basecoat material. Thespecific fractional range then applies only to the preferred group ofcomponents. For the total fraction of components, however, consisting ofcomponents from the preferred group and components which do not fallwithin the preferred group, the specific fractional range likewisepreferably applies.

If, therefore, there were to be restriction to a fractional range of 1.5to 15 wt % and to a preferred group components, then this fractionalrange evidently applies initially only to the preferred group ofcomponents. In that case, however, it would be preferable for there tobe likewise from 1.5 to 15 wt % present overall of all originallyencompassed components, consisting of components from the preferredgroup and components not falling within the preferred group. If,therefore, 5 wt % of components of the preferred group are employed,then not more than 10 wt % of the components of the non-preferred groupcan be used.

In the context of the present invention, the stated principle applies toall stated components of the basecoat material and to their fractionalranges, as for example the aqueous dispersions of the invention,pigments, the polyurethane resins as binders, or else the crosslinkingagents such as melamine resins.

The aqueous basecoat material generally comprises coloring pigmentsand/or optical-effect pigments.

Such color pigments and effect pigments are known to the skilled personand are described in, for example, Römpp-Lexikon Lacke and Druckfarben,Georg Thieme Verlag, Stuttgart, New York, 1998, pages 176 and 451.

Effect pigments are, for example, metallic effect pigments such asaluminum pigments, gold bronzes, oxidized bronzes and/or ironoxide-aluminum pigments, pearlescent pigments such as, for example,pearl essence, basic lead carbonate, bismuth oxide chloride and/or metaloxide-mica pigments and/or other effect pigments such as micronizedtitanium dioxide, lamellar graphite, lamellar iron oxide, multilayereffect pigments formed from PVD films, and/or liquid crystal polymerpigments.

The fraction of the pigments may be for example in the range from 1 to40 wt %, preferably 2 to 20 wt %, more preferably 5 to 15 wt %, based onthe total weight of the pigmented aqueous basecoat material.

Basecoat material of the invention may comprise binders curablephysically, thermally, or both thermally and with actinic radiation.

In the context of the present invention, the term “physical curing”means the formation of a film through loss of solvent from polymersolutions or polymer dispersions. Typically, no crosslinking agents arenecessary for this curing.

In the context of the present invention, the term “thermal curing” meansthe heat-initiated crosslinking of a coating film, with either aseparate crosslinking agent or else self-crosslinking binders beingemployed in the parent coating material. The crosslinking agent containsreactive functional groups which are complementary to the reactivefunctional groups present in the binders. This is commonly referred toby those is the art as external crosslinking. Where the complementaryreactive functional groups or autoreactive functional groups—that is,groups which react with groups of the same kind—are already present inthe binder molecules, the binders present are self-crosslinking.Examples suitable complementary reactive functional groups andautoreactive functional groups are known from German patent application.DE 199 30 665 A1, page 7, line 28 to page 9, line 24.

For the purposes of the present invention, actinic radiation meanselectromagnetic radiation such as near infrared (NIR), UV radiation,more particularly UV radiation, and particulate radiation such aselectron radiation. Curing by UV radiation is commonly initiated byradical or cationic photoinitiators.

Where thermal curing and curing with actinic light are employed inunison, the term “dual cure” is also used.

In the present invention preference is given to basecoat materials whichare curable thermally or both thermally and with actinic radiation,i.e., by “dual cure”.

Especially preferred basecoat materials are those which comprise asbinder a polyacrylate resin and as crosslinking agent an aminoplastresin or a blocked or nonblocked polyisocyanate, preferably anaminoplast resin. Among the aminoplast resins, melamine resins areespecially preferred.

As well as the aqueous dispersion of the invention basecoat materials ofthe invention preferably comprise a further binder, preferably apolyurethane resin.

The polyurethane resin preferably present may be tonically and/ornononically hydrophilically stabilized. In preferred embodiments thepresent invention the polyurethane resin is ionically hydrophilicallystabilized. The preferred polyurethane resins are linear or containinstances of branching. The polyurethane resin is more preferably one inwhose presence olefinically unsaturated monomers have been polymerized.This polyurethane resin may be present alongside the polymer originatingfrom the polymerization of the olefinically unsaturated monomers,without these polymers being bonded covalently to one another. Equally,however, the polyurethane resin may also be bonded covalently to thepolymer originating from the polymerization of the olefinicallyunsaturated monomers. The olefinically unsaturated monomers arepreferably monomers containing acrylate groups and/or methacrylategroups. It likewise preferred for the monomers containing acrylateand/or methacrylate groups to be used in combination with otherolefinically unsaturated compounds which contain no acrylate ormethacrylate groups. Olefinically unsaturated monomers attached to thepolyurethane resin are more preferably monomers containing acrylategroups or methacrylate groups, thereby producing polyurethane(meth)acrylates. Very preferably the polyurethane resin is apolyurethane (meth)acrylate. The polyurethane resin present withpreference is curable physically, thermally, or both thermally and withactinic radiation. More particularly it is curable either thermally orboth thermally and with actinic radiation. With particular preferencethe polyurethane resin comprises reactive functional groups throughwhich external crosslinking is possible.

Suitable saturated or unsaturated polyurethane resins are described, forexample, in

-   -   German patent application DE 199 14 896 A1, column 1, lines 29        to 49 and column 4, line 23 to column 11, line 5,    -   German patent application DE 199 48 004 A1, page 4, line 19 to        page 13, line 48,

European patent application EP 0 228 003 A1, page 3, line 24 to page 5,line 40,

-   -   European patent application EP 0 634 431 A1, page 3, line 38 to        page 8, line 9, or    -   international patent application WO 92/15405, page 2, line 35 to        page 10, line 32,    -   German patent application DE 4437535 A1, page 7, line 55 to page        8, line 23,    -   international patent application WO 91/15528, page 23, line 29        to page line 24.

The polyurethane resin is prepared using preferably the aliphatic,cycloaliphatic, aliphatic-cycloaliphatic, aromatic, aliphatic-aromaticand/or cycloaliphatic aromatic polyisocyanates that are known to theskilled person.

As alcohol component for preparing the polyurethane resins, preferenceis given to using the saturated and unsaturated polyols of relativelyhigh molecular mass and of low molecular mass, and also, optionally,monoalcohols, in minor amounts, that are known to the skilled person.Low molecular mass polyols used are more particularly diols and, inminor amounts, triols, for introducing instances of branching. Examplesof suitable polyols of relatively high molecular mass are saturated orolefinically unsaturated polyester polyols and/or polyether polyols.Relatively high molecular mass polyols used are more particularlypolyester polyols, especially those having a number-average molecularweight of 400 to 5000 g/mol.

For hydrophilic stabilization and/or for increasing the dispersibilityin aqueous medium, the polyurethane resin preferably present may containparticular ionic groups and/or groups which can be converted to ionicgroups (potentially ionic groups). Polyurethane resins of this kind arereferred to in the context of the present invention as ionicallyhydrophilically stabilized polyurethane resins. Likewise present may benonionic hydrophilically modifying groups. Preferred, however, are theionically hydrophilically stabilized polyurethanes. In more preciseterms, the modifying groups are alternatively

-   -   functional groups which can be converted to cations by        neutralizing agents and/or quaternizing agents, and/or cationic        groups (cationic modification) or    -   functional groups which can be converted to anions by        neutralizing agents, and/or anionic groups (anionic        modification) and/or    -   nonionic hydrophilic groups (nonionic modification).

As the skilled person is aware, the functional groups for cationicmodification are, for example, primary, secondary and/or tertiary aminogroups, secondary sulfide groups and/or tertiary phosphine groups, moreparticularly tertiary amino groups and secondary sulfide groups(functional groups which can be converted to cationic groups byneutralizing agents and/or quaternizing agents). Mention should also bemade of the cationic groups—groups prepared from the aforementionedfunctional groups using neutralizing agents and/or quaternizing agentsknown to those skilled in the art such as primary, secondary, tertiaryand/or quaternary ammonium groups, tertiary sulfonium groups and/orquaternary phosphonium groups, more particularly quaternary ammoniumgroups and tertiary sulfonium groups.

As is well known, the functional groups for anionic modification are,for example, carboxylic acid, sulfonic acid and/or phosphonic acidgroups, more particularly carboxylic acid groups (functional groupswhich can be converted to anionic groups by neutralizing agents), andalso anionic groups—groups prepared from the aforementioned functionalgroups using neutralizing agents known to the skilled person—such ascarboxylate, sulfonate and/or phosphonate groups.

The functional groups for nonionic hydrophilic modification arepreferably poly(oxyalkylene) groups, more particularly polyoxyethylene)groups.

The ionically hydrophilic modifications can be introduced into thepolyurethane resin through monomers which contain the (potentially)ionic groups. The nonionic modifications are introduced, for example,through the incorporation of poly(ethylene) oxide polymers as lateral orterminal groups in the polyurethane molecules. The hydrophilicmodifications are introduced, for example, via compounds which containat least one group reactive toward isocyanate groups, preferably atleast one hydroxyl group. The modification can be introduced usingmonomers which, as well as the modifying groups, contain at least onehydroxyl group. To introduce the nonionic modifications, preference isgiven to using the polyether diols and/or alkoxypoly(oxyalkylene)alcohols known to those skilled in the art.

The polyurethane resin may preferably be a graft polymer. Moreparticularly it is a polyurethane resin grafted with olefinicallyunsaturated compounds, preferably olefinically unsaturated monomers. Inthis case, then, the polyurethane is grafted, for example, with sidegroups and/or side chains that are based on olefinically unsaturatedmonomers. These are more particularly side chains based onpoly(meth)acrylates. Poly(meth)acrylates for the purposes of the presentinvention are polymers or polymeric radicals which comprise monomerscontaining acrylate and/or methacrylate groups, and preferably consistof monomers containing acrylate groups and/or methacrylate groups. Sidechains based on poly(meth)acrylates are understood to mean side chainswhich are constructed during the graft polymerization, using monomerscontaining (meth) acrylate groups. In the graft polymerization,preference here is given to using more than 50 mol %, more particularlymore than 75 mol %, especially 100 mol %, based on the total amount ofthe monomers used in the graft polymerization, of monomers containing(meth)acrylate groups.

The side chains described are introduced into the polymer preferablyafter the preparation of a primary polyurethane resin dispersion. Inthis case the polyurethane resin present in the primary dispersion maycontain lateral and/or terminal olefinically unsaturated groups viawhich, then, the graft polymerization with the olefinically unsaturatedcompounds proceeds. The polyurethane resin for grafting may therefore bean unsaturated polyurethane resin (A). The graft polymerzation is inthat case a radical polymerization of olefinically unsaturatedreactants. Also possible, for example, is for the olefinicallyunsaturated compounds used for the graft polymerization to contain atleast one hydroxyl group. In that case it is also possible first forthere to be attachment of the olefinically unsaturated compounds viathese hydroxyl groups through reaction with free isocyanate groups ofthe polyurethane resin. This attachment takes place instead of or inaddition to the radical reaction of the olefinically unsaturatedcompounds with the lateral and/or terminal olefinically unsaturatedgroups optionally present in the polyurethane resin. This is thenfollowed again by the graft polymerization via radical polymerization,as described earlier on above. The result in any case is polyurethaneresins grafted with olefinically unsaturated compounds, preferablyolefinically unsaturated monomers.

As olefinically unsaturated compounds with which the polyurethane resin(A) is preferably grafted it is possible to use virtually all radicallypolymerizable, olefinically unsaturated, and organic monomers which areavailable to the skilled person for these purposes. A number ofpreferred monomer classes may be specified by way of example:

-   -   hydroxyalkyl esters of (meth)acrylic acid or of other        alpha,beta-ethylenically unsaturated carboxylic acids,    -   (meth)acrylic acid alkyl and/or cycloalkyl esters having up to        20 carbon atoms in the alkyl radical,    -   ethylenically unsaturated monomers comprising at least one acid        group, more particularly exactly one carboxyl group, such as        (meth)acrylic acid, for example,    -   vinyl esters of monocarhoxylic acids which are branched in        alpha-position and have 5 to 18 carbon atoms,    -   reaction products of (meth)acrylic acid with the glycidyl ester        of a monocasboxylic acid which branched in alpha-position and        has 5 to 18 carbon atoms,    -   further ethylenically unsaturated monomers such as olefins        (ethylene for example), (meth)acrylamides, vinylaromatic        hydrocarbons (styrene for example), vinyl compounds such as        vinyl chloride and/or vinyl ethers such as ethyl vinyl ether.

Used with preference are monomers containing (meth)acrylate groups, andso the side chains attached by grafting are poly(meth)acrylate-basedside chains.

The lateral and/or terminal olefinically unsaturated groups in thepolyurethane resin, via which the graft polymerization with theolefinically unsaturated compounds can proceed, are introduced into thepolyurethane resin preferably via particular monomers. These particularmonomers, in addition to an olefinically unsaturated group, alsoinclude, for example, at least one group that is reactive towardisocyanate groups. Preferred are hydroxyl groups and also primary andsecondary amino groups. Especially preferred are hydroxyl groups.

The monomers described through which the lateral and/or terminalolefinically unsaturated groups may be introduced into the polyurethaneresin may also, of course, be employed without the polyurethane resinbeing additionally grafted thereafter with olefinically unsaturatedcompounds. It is preferred, however, for the polyurethane resin to begrafted with olefinically unsaturated compounds.

The polyurethane resin preferably present may be a self-crosslinkingand/or externally crosslinking binder. The polyurethane resin preferablycomprises reactive functional groups through which external crosslinkingis possible. In that case there is preferably at least one crosslinkingagent in the pigmented aqueous basecoat material. The reactivefunctional groups through which external crosslinking is possible aremore particularly hydroxyl groups. With particular advantage it ispossible, for the purposes of the method of the invention, to usepolyhydroxy-functional polyurethane resins. This means that thepolyurethane resin contains on average more than one hydroxyl group permolecule.

The polyurethane resin is prepared by the customary methods of polymerchemistry. This means, for example, the polyaddition of polyisocyanatesand polyols to polyurethanes, and the graft polymerization thatpreferably then follows with olefinically unsaturated compounds. Thesemethods are known to the skilled person and can be adapted individually.Exemplary preparation processes and reaction conditions can be found inEuropean patent EP 0521 928 E1, page 2, line 57 to page 8, line 16.

The polyurethane resin preferably present preferably possesses anumber-average molecular weight of 200 to 30,000 g/mol, more preferablyof 2000 to 20,000 g/mol. It further possesses, for example, a hydroxylnumber of 0 to 250 mg KOH/g, but more particularly from 20 to 150 mgKOH/g. The acid number of the polyurethane resin is preferably 5 to 200mg KOH/g, more particularly 10 to 40 mg KOH/g. For the purposes of thepresent invention, the hydroxyl number is determined to DIN 53240, andthe acid number to DIN 53402.

The aqueous basecoat material of the invention may further comprise atleast one polyester, more particularly a polyester having anumber-average molecular weight of 400 to 5000 g/mol, as binder. Suchpolyesters are described for example in DE 4009858 in column 6, line 53to column 7, line 61 and column 10, line 24 to column 13, line 3

There is preferably also at least one thickener present. Suitablethickeners are inorganic thickeners from the group of thephyllosilicates. Particularly suitable are lithium aluminum magnesiumsilicates.

As well as the inorganic thickeners, however, it is also possible to useone or more organic thickeners. These are preferably selected from thegroup consisting of (meth) acrylic acid-(meth)acrylate copolymerthickeners, for example the commercial product Rheovis® AS 1130 (BASFSE), and of polyurethane thickeners, for example the commercial productRheovis® PU 1250 from BASF SE. (Meth)acrylic acid-(meth)acrylatecopolymer thickeners are those which as well as acrylic acid and/ormethacrylic acid also contain in copolymerized form one more acrylicesters (i.e., acrylates) and/or one or more methacrylcic esters (i.e.,methacrylates). A feature common to the (meth)acrylicacid-(meth)acrylate copolymer thickeners is that in an alkaline medium,in other words at pH levels >7, more particularly >7.5, by formation ofa salt of the acrylic acid and/or methacrylic acid, in other words bythe formation of carboxylate groups, they exhibit a strong increase inviscosity. If (meth)acrylic esters are used which are formed from(meth)acrylic acid and a C₁-C₆ alkanol, the products are essentiallynonassociative (meth) acrylic acid-(meth)acrylate copolymer thickeners,such as the abovementioned Rheovis AS 1130, for example. Essentiallynonassociative (meth) acrylic acid-(meth)acrylate copolymer thickenersare also referred to in the literature as ASE thickeners (“AlkaliSoluble/Swellable Emulsion” or dispersion.). Also possible for use as(meth) acrylic acid-(meth)acrylate copolymer thickeners, however, arethose known as HASE thickeners (“Hydrophobically Modified AnionicSoluble Emulsions” or dispersion). These are obtained by using asalkanols, instead of or in addition to the C₁-C₆ alkanols, those havinga larger number of carbon atoms, as for example 7 to 30, or 8 to 20carbon atoms. HASE thickeners have an essentially associative thickeningeffect. On account of their thickening properties, the (meth)acrylicacid-(meth) acrylate copolymer thickeners which can be used are not,suitable as binder resins, and hence do not come under the physically,thermally, or both thermally and actinically curable binders that areidentified as binders, and they are therefore explicitly different fromthe poly(meth)acrylate-based binders which can be employed in thebasecoat material compositions of the invention. Polyurethane thickenersare the associative thickeners that are identified in the literature asHEUR (“Hydrophobically Modified Ethylene Oxide Urethane RheologyModers”). Chemically these are nonionic, branched or unbranched, blockcopolymers composed of polyethylene oxide chains (sometimes alsopolypropylene oxide chains) which are linked to one another via urethanebonds and which carry terminal long-chain alkyl or alkylene groupshaving 8 to 30 carbon atoms. Typical alkyl groups are, for example,dodecyl or stearyl groups; a typical alkenyl group is, for example, anoleyl group; a typical aryl group is the phenyl group; and a typicalalkylated aryl group is, for example, a nonylphenyl group. On account oftheir thickening properties and structure, the polyurethane thickenersare not suitable as binder resins curable physically, thermally, or boththermally and physically. They are therefore explicitly different fromthe polyurethanes which can be used as binders in the basecoat materialcompositions of the invention.

Furthermore, the aqueous basecoat material may further comprise at leastone adjuvant. Examples of such adjuvants are salts which can bedecomposed thermally without residue or substantially without residue,resins as binders that are curable physically, thermally and/or withactinic radiation and are different from polyurethane resins, furthercrosslinking agents, organic solvents, reactive diluents, transparentpigments, molecularly dispersely soluble dyes, nanoparticles, lightstabilizers, antioxidants, deaerating agents, emulsifiers, slipadditives, polymerization inhibitors, initiators or radicalpolymerizations, adhesion promoters, flow control agents, film-formingassistants, sag control agents (SCAs), flame retardants, corrosioninhibitors, waxes, siccatives, biocides, and flatting agents.

Suitable adjuvants of the aforementioned kind are known, for example,from

-   -   German patent application DC 199 48 004 A1, page 14, line 4 to        page 17, line 5,    -   German patent DC 100 43 405 C1 column 5, paragraphs [0031] to        [0033]. They are used in the customary and known amounts.

The solids content of the basecoat materials of the invention may varyaccording to the requirements of the case in hand. The solids content isguided primarily by the viscosity required for application, moreparticularly for spray application, and so may be adjusted by theskilled person on the basis of his or her general art knowledge,optionally with assistance from a few exploratory tests.

The solids content of the basecoat materials preferably 5 to 70 wt %,more preferably 10 to 65 wt %, and especially preferably 15 to 60 wt %.

The basecoat material of the invention is aqueous. The expression“aqueous” is known in this context to the skilled person. The phraserefers is principle to a basecoat material which is not basedexclusively on organic solvents, i.e., does not contain exclusivelyorganic-based solvents as its solvents but instead, in contrast,includes a significant fraction of water as solvent. “Aqueous” for thepurposes of the present invention, in relation to coating compositions,should preferably be understood to mean that the coating composition inquestion, more particularly the basecoat material, has a water fractionof at least. 40 wt %, preferably at least 50 wt %, very preferably atleast 60 wt %, based in each case on the total amount of the solventspresent (i.e., water and organic solvents). Preferably in turn, thewater fraction is 40 to 90 wt %, more particularly 50 to 80 wt %, verypreferably 60 to 75 wt %, based in each case on the total amount of thesolvents present.

The basecoat materials employed in accordance with the invention may beproduced using the mixing assemblies and mixing techniques that arecustomary and known for producing basecoat materials.

The Process of the Invention and the Multicoat Paint System of theInvention

A further aspect of the present invention is a process for producing amulticoat paint system, where

-   (1) a pigmented aqueous basecoat material is applied to a substrate,-   (2) a polymer film is formed from the coating material applied in    stage (1),-   (3) a clearcoat material is applied to the resulting basecoat film,    and then-   (4) the basecoat film is cured together with the clearcoat film,

which comprises using in stage (1) a pigmented aqueous basecoat materialwhich comprises at least one aqueous dispersion of the invention. All ofthe above observations relating to the dispersion of the invention andto the pigmented aqueous basecoat material are also valid in respect ofthe process of the invention. This is true more particularly also of allpreferred, very preferred, and especially preferred features.

Said process is preferably used to produce multicoat color paintsystems, effect paint systems, and color and effect paint systems.

The pigmented aqueous basecoat material of the invention is commonlyapplied to metallic or plastics substrates that have been pretreatedwith surfacer or primer-surfacer. Said basecoat material may optionallyalso be applied directly to the plastics substrate.

Where a metallic substrate is to be coated, it is preferably furthercoated with an electrocoat system before the surfacer or primer-surfaceris applied.

Where a plastics substrate is being coated, preferably also pretreatedbefore the surfacer or primer-surfacer applied. The techniques mostfrequently employed for such pretreatment are those of flaming, plasmatreatment, and corona discharge. Flaming is used with preference.

Application of the pigmented aqueous basecoat material of the inventionto a metallic substrate may take place in the film thicknesses customarywithin the automobile industry, in the range, for example, of 5 to 100micrometers, preferably 5 to 60 micrometers. This is done using sprayapplication methods, for example compressed air spraying, airlessspraying, high-speed rotation, electrostatic spray application (ESTA),alone or in conjunction with hot spray application, for example hot airspraying.

Following the application of the pigmented aqueous basecoat material, itcan be dried by known methods. For example, (1-component) basecoatmaterials, which are preferred, can be flashed at room temperature for 1to 60 minutes and subsequently dried, preferably at optionally slightlyelevated temperatures of 30 to 90° C. Flashing and drying in the contextof the present invention mean the evaporation of organic solvents and/orwater, as a result of which the paint becomes drier but has not yetcured or not yet formed a fully crosslinked coating film.

Then a commercial clearcoat material is applied, by likewise commonmethods, the film thicknesses again being within the customary ranges,for example 5 to 100 micrometers.

After the clearcoat material has been applied, it can be flashed at roomtemperature for 1 to 60 minutes, for example, and optionally dried. Theclearcoat material is then cured together with the applied pigmentedbasecoat material. In the course of these procedures, crosslinkingreactions occur, for example, to produce on a substrate a multicoatcolor and/or effect paint system of the invention. Curing takes placepreferably thermally at temperatures from 60 to 200° C. Thermally curingbasecoat materials are preferably those which comprise as crosslinkingagent an aminoplast resin or a blocked or nonblocked polyisocyanate,preferably an aminoplast resin. Among the aminoplast resins, melamineresins are preferred.

Plastics substrates are coated basically in the same way as metallicsubstrates. Here, however, in general, curing takes place atsignificantly lower temperatures, of 30 to 90° C. Preference istherefore given to the use of two-component clearcoat materials.

The process of the invention can be used to paint metallic andnonmetallic substrates, more particularly plastics substrates,preferably automobile bodies or parts thereof.

The process of the invention can be used further for dual finishing inOEM finishing. This means that a substrate which has been coated bymeans of the process of the invention is painted for a second time,likewise by means of the process of the invention.

The invention relates further to multicoat paint systems which areproducible by the process described above. These multicoat paint systemsare to be referred to below as multicoat paint systems of the invention.

All of the above observations relating to the polymer of the invention,to the pigmented aqueous basecoat material, and to the method of theinvention are also valid in respect of said multicoat paint system. Thisis also true especially of all the preferred, more preferred, and mostpreferred features.

The multicoat paint systems of the invention are preferably multicoatcolor paint systems, effect paint systems, and color and effect paintsystems.

A further aspect of the invention relates to the process of theinvention, wherein said substrate from stage (1) is a multicoat paintsystem having defect sites. This substrate/multicoat paint whichpossesses defect sites, is therefore an original finish, which is to berepaired or completely recoated.

The process of the invention is suitable accordingly for repairingdefects on multicoat paint systems. Film defects are generally faults onand in the coating, usually named according to their shape or theirappearance. The skilled person is aware of a host of possible kinds ofsuch film defects. They are described for example in Römpp-Lexikon Lackeand Druckfarben, Georg Thieme Verlag, Stuttgart, New York, :1998, page235, “Film defects”.

In one preferred embodiment of the process of the invention, thesubstrate from stage (1) is a multicoat paint system which has defectsites.

These multicoat paint systems are produced preferably on automobilebodies or parts thereof, by means of the process of the invention,identified above, in the context of automotive OEM finishing. Where suchdefects occur directly after OEM finishing has taken place, they arerepaired immediately. The term “OEM automotive refinishing” is thereforealso used. Where only small defects require repair, only the “spot” isrepaired, and the entire body is not completely recoated (dual coating).The former process is called “spot repair”. The use of the process ofthe invention for remedying defects on multicoat paint systems (originalfinishes) of the invention in OEM automotive refinishing, therefore, isparticularly preferred.

Where reference is made, in the context of the present invention, to theautomotive refinish segment, in other words when the repair of defectsis the topic, and the substrate specified is a multicoat paint systempossessing defects, this of course means that this substrate/multicoatpaint system with defects (original finish) is generally located on aplastic substrate or on a metallic substrate as described above.

So that the repaired site has no color difference from the rest of theoriginal finish, it is preferred for the aqueous basecoat material usedin stage (1) of the process of the invention for repairing defects to bethe same as that which was used to produce the substrate/multicoat paintsystem with defects (original finish).

The observations above concerning the polymer of the invention and theaqueous pigmented basecoat material therefore are also valid for theuse, under discussion, of the process of the invention for repairingdefects on a multicoat paint system. This is also true in particular ofall stated preferred, very preferred, and especially preferred features.It is additionally preferred for the multicoat paint systems of theinvention that are to be repaired to be multicoat color paint systems,effect paint systems, and color and effect paint systems.

The above-described defect sites on the multicoat paint system of theinvention can be repaired means of the above-described process theinvention. For this purpose, the surface to be repaired on the multicoatpaint system may initially be abraded. The abrading is preferablyperformed by partially sanding, or sanding off, only the basecoat andthe clearcoat from the original finish, but not sanding off the primerlayer and surfacer layer that are generally situated beneath them. Inthis way, during the refinish, there is no need in particular forrenewed application of specialty primers and primer-surfacers. This formof abrading has become established especially in the OEM automotiverefinishing segment, since here, in contrast to refinishing in aworkshop, generally speaking, defects occur only in the basecoat and/orclearcoat region, but do not, in particular, occur in the region of theunderlying surfacer and primer coats. Defects in the latter coats aremore likely to be encountered in the workshop refinish sector. Examplesinclude paint damage such as scratches, which are produced, for example,by mechanical effects and which often extend down to the substratesurface (metallic or plastic substrate).

After the abrading procedure, the pigmented aqueous basecoat material isapplied to the defect site in the original finish, generally bypneumatic atomization. After the pigmented aqueous basecoat material hasbeen applied, it can be dried by known methods. For example, thebasecoat material may be dried at room temperature for 1 to 60 minutesand subsequently dried at optionally slightly elevated temperatures of30 to 80° C. Flashing and drying for the purposes of the presentinvention means evaporation of organic solvents and/or water, wherebythe coating material is as yet riot fully cured. For the purposes of thepresent invention it is preferred for the basecoat material to comprisean aminoplast resin, preferably a melamine resin, as crosslinking agent,and a binder that is reactive with this crosslinking agent.

A commercial clearcoat material is subsequently applied, by techniquesthat are likewise commonplace. Following application of the clearcoatmaterial, it may be flashed off at room temperature for 1 to 60 minutes,for example, and optionally dried. The clearcoat material is then curedtogether with the applied pigmented basecoat material.

In the case of so-called low-temperature baking, curing takes placepreferably at temperatures of 20 to 90° C. Preference here is given tousing two-component clearcoat materials. If, as described above, anaminoplast resin is used as crosslinking agent, there is only slightcrosslinking by the aminoplast resin in the basecoat film at thesetemperatures. Here, in addition to its function as a curing agent, theaminoplast resin also serves for plasticizing and may assist pigmentwetting. Besides the aminoplast resins, nonblocked isocyanates may alsobe used. Depending on the nature of the isocyanate used, they crosslinkat temperatures from as low as 20° C.

In the case of what is called high-temperature baking, curing isaccomplished preferably at temperatures of 130 to 150° C. Here bothone-component and two-component clearcoat materials are used. If, asdescribed above, an aminoplast resin is used as crosslinking agent,there is crosslinking by the aminoplast resin in the basecoat film atthese temperatures.

For repairing defects on multicoat paint systems, in other words whenthe substrate is an original finish with defects, preferably a multicoatpaint system of the invention that exhibits defects, low-temperaturebaking is preferably employed.

A further aspect of the present invention is the use of the aqueousdispersions of the invention in pigmented aqueous basecoat materials forimproving adhesion.

The aqueous dispersions of the invention can be used for improvingadhesion in the finishing of metallic and plastics substrates. They canalso be employed in automotive refinishing. By automotive refinishing ismeant both OEM automotive refinishing and the auto motive refinishingthat takes place in a workshop, for example.

Where said pigmented aqueous basecoat materials are used in thefinishing of metallic and plastics substrates, the use of the aqueousdispersion of the invention results in particular in an improvement inthe adhesion between the basecoat film and the clearcoat film that isimmediately adjacent to it. The dispersion of the invention is thereforeused with preference for improving adhesion between basecoat film andclearcoat film in the finishing of metallic substrates and plasticssubstrates.

Where said pigmented aqueous basecoat materials are used in automotiverefinishing, the use of the aqueous dispersion of the invention resultsin particular in an improvement in adhesion between basecoat andoriginal finish. The aqueous dispersion of the invention is thereforelikewise used with preference for improving the adhesion betweenbasecoat film and original finish automotive refinishing, morepreferably in OEM automotive refinishing.

The adhesion difficulties affecting systems of the prior art areespecially striking when the coated substrates are exposed toweathering. Corresponding weathering conditions can be simulated bycondensing water storage. The term “condensing water storage” denotesthe storage of coated substrates in a climatic chamber in accordancewith CH test conditions in accordance with DIN EN ISO 6270-2:2005-09.

The aqueous dispersions of the invention are therefore also used inparticular to improve the adhesion after condensation water storage. Theadhesion is investigated preferably in a steam jet test according totest method A of DIN 55662:2009-12.

When coated substrates are exposed to weathering, blisters and swellingare a common occurrence. The aqueous dispersions of the invention aretherefore also used in particular to reduce or prevent the incidence ofblisters and swelling in multicoat paint systems.

The presence of blisters and swelling can be appraised visually.

The invention is elucidated below in the form of examples.

The inventive and comparative examples which follow serve to elucidatethe invention, but should not be interpreted as imposing anyrestriction.

INVENTIVE AND COMPARATIVE EXAMPLES

Unless otherwise indicated, the amounts in parts are parts by weight andamounts in percent are in each case percentages by weight.

1. Components Employed

The definitions of the components identified below and used in preparingthe dispersions of the invention and also the waterborne basecoatmaterials of the invention comprising the dispersions of the inventionas binders, and the corresponding comparative examples, are as follows:

Aerosol® EF-800 is a commercially available emulsifier from Cytec.

APS is used as an abbreviation of the chemical compound ammoniumperoxodisulfate.

1,6-HDDA is used as an abbreviation of the chemical compound.1,6-nexanediol diacrylate.

VEOVA™10 is a commercially available monomer from Momentive. The monomeris the vinyl ester of Versatic™Acid 10.

2-HEA is used as as abbreviation of the chemical compound 2-hydroxyethylacrylate.

MMA is used as as abbreviation of the chemical compound methylmethacrylate.

Sipomer PAM 200 is a commercially available phosphate ester ofpolypropylene glycol moan ethyl acrylate from Solvay.

DMEA is used as an abbreviation of the chemical compounddimethylethanolamine.

Rhodapex® CO 436 is a commercially available emulsifier from Solvay,Rhodia.

Cymel® 303 is a commercially available melamine-formaldehyde resin fromAllnex.

Rheovis® AS 1130 is a commercially available rheology additive foraqueous coating materials, from BASF SE.

Pluriol® E300 is a commercially available polyethylene glycol from BASESE.

2. Examples of Syntheses of the Aqueous Dispersions Comprising at LeastOne Multistage Polymer 2.1 Preparation of Aqueous Dispersions BM1, BM2,and BM3, Comprising a Seed-Core-Shell Acrylate SCS1, SCS2, and SCS3(Inventive)

80 wt % of items 1 and 2 in table 2.1 are placed into a steel reactor (511, volume) with reflux condenser, and heated to 80° C., The remainingfractions of the components listed under “initial charge” in table 2.1are premixed in a separate vessel. This mixture and the initiatorsolution are added dropwise to the reactor over 20 minutes, where amonomers concentration of 6.0 wt % in the reaction solution is notexceeded throughout the reaction period. This is followed by stirringfor 30 minutes. (Corresponds to stage i).)

The components indicated under “mono 1” in table 2.1 are premixed in aseparate vessel. This mixture is added dropwise to the reactor over 2hours, where a monomers concentration or 6.0 wt % in the reactionsolution is not exceeded throughout the reaction period. This isfollowed by 1 hour of stirring. (Corresponds to stage ii).)

The components indicated under “mono 2” in table 2.1 are premixed in aseparate vessel. This mixture is added dropwise to the reactor over 1hour, where a monomers concentration or in the reaction period. Thisfollowed by 2 hours or stirring. (Corresponds to stage iii).)

The reaction mixture is thereafter cooled to 60° C. and the neutralizingmixture is premixed in a separate vessel. The neutralizing mixture isadded dropwise to the reactor over 40 minutes, wherein the pH of thereaction solution is adjusted to a pH of 6.5 to 9.0. The reactionproduct is subsequently stirred for 30 minutes more, cooled to 25° C.and filtered. (Corresponds to stage iv).)

TABLE 2.1 Aqueous dispersions BM1 to BM3 comprising seed-core-shellacrylates SCS1 to SCS3 (according to the invention) BM1 BM2 BM3 Initialcharge 1 DI water 43.54 43.54 41.81 2 EF 800 0.18 0.19 0.18 3 Styrene0.5 0.5 0.48 4 n-Butyl acrylate 0.68 5 Ethyl acrylate 0.55 0.55Initiator solution 6 DI water 0.55 0.53 0.53 7 APS 0.02 0.02 0.02 Mono 18 DI water 13.31 13.31 12.78 9 EF 800 0.15 0.15 0.15 10 APS 0.02 0.020.02 11 Styrene 5.84 5.84 5.61 12 n-Butyl acrylate 13.6 13 Ethylacrylate 11.05 9.47 14 1,6-HDDA 0.35 0.35 0.34 15 VEOVA ™10 1.58 Mono 216 DI water 5.97 5.97 5.73 17 EF 800 0.07 0.07 0.07 18 APS 0.02 0.020.02 19 Methacrylic acid 0.74 0.74 0.71 20 2-HEA 0.31 0.99 0.85 21n-Butyl acrylate 1.87 22 Ethyl acrylate 3.04 3.04 23 MMA 0.6 0.58 24Sipomer PAM 0.68 25 VEOVA ™10 1.87 Neutralizing 26 DI water 6.75 6.756.48 27 Butyl glycol 4.96 4.96 4.76 28 DMEA 0.79 0.79 0.76 pH 7.2 8.58.2

The solids content was determined for the purpose of reactionmonitoring. The results are reported in table 2.2:

TABLE 2.2 Solids content of the aqueous dispersions BM1 to BM3 BM1 BM2BM3 Solids content 23.7 21.5 25.4

After each stage i) to iv), the particle size of the polymers wasdetermined by means of dynamic light scattering in accordance with DINISO 13321. The results are reproduced in table 2.3.

TABLE 2.3 Particle sizes in nm of the seed-core-shell acrylates SCS1 toSCS3 after each stage i) to iv) SCS1 SCS2 SCS3 i After “initial charge”60 70 70 ii After “Mono 1” 140 130 153 iii After “Mono 2” 210 212 194 ivAfter neutralizing 236 225 236

Each of the stated monomer mixtures was polymerized individually andthereafter the glass transition temperature was determined by means ofDSC in accordance with DIN standard 53765. Also determined was the glasstransition temperature for the overall polymer, after neutralization, bymeans of DSC in accordance with DIN standard 53765.

The results are reported in table 2.4.

TABLE 2.4 Glass transition temperatures in ° C. of individual stages ofthe seed-core-shell acrylates SCS1 to SCS3 SCS1 SCS2 SCS3 i “Initialcharge” 33 36 32 ii “Mono 1” −12 −15 −11 iii “Mono 2” 9 −1 −5 Overallpolymer −8 −10 −112.2 Preparation of an Aqueous Dispersion BM5 Comprising a Three-StageAcrylate SCS5 (as per Korea Polym. J., vol. 7, no. 4, pp. 213-222; notInventive)

Components 1 to 4 from table 2.5 are placed into a steel reactor (5 Lvolume) with reflux condenser, and heated to 80° C. The initiatorsolution (table 2.5, items 5 and 6) is added dropwise to the reactorover 5 minutes. This is followed by stirring for 30 minutes.

The components indicated under “mono 1” in table 2.5 are premixed in aseparate vessel. This mixture is added dropwise to the reactor over 2hours. This is followed by 1 hour of stirring.

The components indicated under “mono 2” in table 2.5 are premixed in aseparate vessel. This mixture is added dropwise to the reactor over 1hour. This is followed by 1 hour of stirring.

The reaction mixture is thereafter cooled to 60° C. and the neutralizingmixture (table 2.5, items 20 to 22) is premixed in a separate vessel.The neutralizing mixture is added dropwise to the reactor over 40minutes. The reaction product is subsequently stirred for 30 minutesmore and cooled to 25° C.

TABLE 2.5 Multistage acrylate BM5 BM5 Initial charge 1 DI water 43.54 2Rhodapex CO 436 0.16 3 Styrene 0.5 4 Ethyl acrylate 0.55 Initiatorsolution 5 DI water 0.55 6 APS 0.02 Mono 1 7 DI water 13.31 8 RhodapexCO 436 0.13 9 APS 0.02 10 Styrene 5.84 11 Ethyl acrylate 11.05 121,6-HDDA 0.35 Mono 2 13 DI water 5.97 14 Rhodapex CO 436 0.06 15 APS0.02 16 Methacrylic acid 0.74 17 2-HEA 0.99 18 Ethyl acrylate 3.04 19MMA 0.6 Neutralizing 20 DI water 6.75 21 Butyl glycol 4.96 22 DMEA 0.79pH 8.1

The solids content was 23.4%.

After each stage i) to iv), the particle size of the polymer wasdetermined by means of dynamic light scattering in accordance with DINISO 13321. The results are reproduced in table 2.6.

TABLE 2.6 Particle sizes in nm of the acrylate SCS5 after each stage i)to iv) SCS5 i After “initial charge” 110 ii After “Mono 1” 196 iii After“Mono 2” 223 iv After neutralizing 310

Each of the stated monomer mixtures was polymerized individually andthereafter the glass transition temperature was determined by means ofDSC in accordance with DIN standard 53765. Also determined was the glasstransition temperature for the overall polymer, after neutralization, bymeans of DSC in accordance with DIN standard 53765.

The results are reported in table 2.7.

TABLE 2.7 Glass transition temperatures in ° C. of the individual stagesof the multistage acrylate SCS5 SCS5 i “Initial charge” 32 ii “Mono 1”26 iii “Mono 2” 35 Overall polymer 26

3. Examples of Paint Formulations

3.1 Preparation of the Noninventive Waterborne Basecoat Materials A1 andA2 Based on the Aqueous Dispersion BM5 (as per Korea Polym. J., vol. 7,no. 4, pp. 213-222)

The components listed under “aqueous phase” in table 3.1 are stirredtogether in the order stated to form an aqueous mixture. In the nextstep, an organic mixture is prepared from the components listed under“organic phase”. The organic mixture is added to the aqueous mixture.This is followed by stirring for 10 minutes, and then a pH of 8 and aspray viscosity of 90-95 mPa·s under a shearing load of 1000 s⁻¹, asmeasured using a rotary viscometer (Rheolab QC instrument withC-LTD80/QC heating system, from Anton Paar) at 23° C. are set usingdeionized water and dimethylethanolamine.

TABLE 3.1 Waterborne basecoat materials A1 and A2 (not inventive) A1 A2Aqueous phase 3% strength Na—Mg phyllosilicate 10.00 solution Aqueousdispersion BM5 (as per 28.40 28.40 Korea. Polym. J., vol. 7, no. 4, pp.213-222) Deionized water 30.30 39.30 Polyester prepared as per 2.70 2.70example D, column 16, lines 37-59 of DE 40 09 858 A1 n-Butoxypropanol3.20 3.20 Melamine-formaldehyde resin 3.20 3.20 (Cymel ® 303 fromAllnex) 10% strength 2.30 2.30 dimethylethanolamine in waterPolyurethane-modified 3.60 3.60 polyacrylate, prepared as per page 7,line 55 to page 8, line 23 of DE 4437535 A1 Rheovis ® AS 1130 (availablefrom 1.50 2.50 BASF SE) Organic phase Butyl glycol 7.00 7.00 Pluriol ®E300 from BASF SE 2.80 2.80 Aluminum pigment available from 5.00 5.00Altana-Eckart (Alu Stapa Hydrolux 8154)

3.2 Preparation of the Inventive Waterborne Basecoat Materials A3 and A4Based on the Aqueous Dispersion BM1

The components listed under “aqueous phase” is table 3.2 are stirredtogether in the order stated to form an aqueous mixture. In the nextstep, an organic mixture is prepared from the components listed under“organic phase”. The organic mixture is added to the aqueous mixture.This is followed by stirring for 10 minutes, and a pH of 8 and a sprayviscosity of 100±5 mPa·s (A3) or 140±5 mPa·s (AA) under a shearing loadof 1000 s⁻¹, measured using a rotary viscometer (Rheolab QC instrumentwith C-LTD80/QC heating system, from Anton Paar) at 23° C., are setusing deionized water and dimethylethanolamine.

TABLE 3.2 Inventive aqueous basecoat materials A3 and A4 A3 A4 Aqueousphase 3% strength Na—Mg 10.00 phyllosilicate solution Aqueous dispersionBM1 30.05 30.05 Deionized water 29.15 20.35 Polyester prepared as per2.70 2.70 example D, column 16, lines 37-59 of DE 40 09 858 A1n-Butoxypropanol 3.20 3.20 Melamine-formaldehyde resin 3.20 3.20(Cymel ® 303 from Allnex) Deionized water 10.00 10.00Polyurethane-modified 3.60 3.60 polyacrylate; prepared as per page 7,line 55 to page 8, line 23 of DE 4437535 A1 Rheovis ® AS 1130 (available1.50 1.30 from BASF SE) 10% strength dimethyl- 1.80 0.80 ethanolamine inwater Organic phase Butyl glycol 7.00 7.00 Pluriol ® E300 from BASF SE2.80 2.80 Aluminum pigment available 5.00 5.00 from Altana-Eckart (AluStapa Hydrolux 8154)

3.3 Preparation of the Inventive Waterborne Basecoat Materials A6 and A7Based on the Inventive Aqueous Dispersions BM2 and BM3

The components listed under “aqueous phase” in table 3.3 are stirredtogether in the order stated to form an aqueous mixture. In the nextstep, an organic mixture is prepared from the components listed under“organic phase”. The organic mixture is added to the aqueous mixture.This is followed by stirring for 10 minutes, and then a pH of 8 and aspray viscosity of 120±5 mPa·s (A6 and A7) under a shearing load of 1000s⁻¹, as measured using a rotary viscometer (Rheolab QC instrument withC-2TD80/QC heating system, from. Anton Pant) at 23° C. are set usingdeionized water and dimethylethanolamine.

TABLE 3.3 Inventive waterborne basecoat materials A6 and A7 A6 A7Aqueous phase 3% strength Na—Mg 10.00 10.00 phyllosilicate solutionAqueous dispersion BM2 30.45 Aqueous dispersion BM3 26.15 Deionizedwater 19.50 23.80 Polyester prepared as per 2.70 2.70 example D, column16, lines 37-59 of DE 40 09 858 A1 n-Butoxypropanol 3.20 3.20Melamine-formaldehyde resin 3.20 3.20 (Cymel ® 303 from Allnex)Deionized water 10.00 10.00 Polyurethane-modified 3.60 3.60polyacrylate; prepared as per page 7, line 55 to page 8, line 23 of DE4437535 A1 Rheovis ® AS 1130 (available 1.75 1.75 from BASF SE) 10%strength dimethyl- 0.80 0.80 ethanolamine in water Organic phase Butylglycol 7.00 7.00 Pluriol ® E300 from BASF SE 2.80 2.80 Aluminum pigmentavailable 5.00 5.00 from Altana-Eckart (Alu Stapa Hydrolux 8154)

Results 4.1 Descriptions of Methods 4.1.1 Determination of Lightness andFlop Index

For determining the lightness or the flop index, an inventive coatingcomposition (or a comparative coating composition) is applied by meansof dual application as waterborne basecoat material to a steel panelcoated with a primer-surfacer coating and having dimensions of 3×60 cm,where, in the first step, application takes place electrostatically witha dry film thickness of 8-9 μm, and in the second step, applicationtakes place after a 2-minute flashing time at room temperature (18 to23° C.), pneumatically with a dry film thickness of 4-5 μm. Theresulting waterborne basecoat film is subsequently dried, after afurther flashing time of 5 minutes at room temperature, in a forced airoven at 80° C. for 5 minutes. Applied over the dried waterborne basecoatfilm is a commercial two-component clearcoat material (ProGloss® fromBASF Coatings GmbH), with a dry film thickness of 40-45 μm. Theresulting clearcoat film is flashed at room temperature (18 to 23° C.)for a period of 10 minutes, followed by curing in a forced air oven at140° C. for 20 minutes more. The substrate coated accordingly issubjected to measurement using an X-Rite spectrophotometer (X-Rite MA68multi-angle spectrophotometer). In this case, the surface is illuminatedusing a light source. Spectral detection in the visible range is carriedout from different angles. From the resulting spectral measurements itis possible, with incorporation of the standard spectral values and alsoof the reflection spectrum of the light source used, to calculate colorvalues in the CIEL*a*b* color space, where L* characterizes thelightness, a* the red-green value, and b* the yellow-blue value. Thismethod is described in ASTM E2194-12, for example, particularly forcoatings comprising at least one effect pigment as pigment. The derivedvalue which is often employed to quantify the metallic effect is theso-called flop index, which describes the relationship between lightnessand observation angle (cf. A. B. J. Rodriguez, JOCCA, 1992 (4), pp.150-153). The flop index (FL) can be calculated from the lightnessvalues found for the viewing angles of 15°, 45°, and 110°, in accordancewith the formula

FL=2.69(L* _(15°) −L* _(110°))^(1.11)/(L* _(45°))^(0.86)

where L* is the lightness value measured at the respective measurementangle (15°45°, and 110°).

4.1.2 Assessment of Appearance Before and After Condensation Exposure

The leveling or waviness of the coated substrates is assessed using aWave scan instrument from Byk/Gardner. The coated substrates areproduced by dual application as described in section 4.1.1 (Determiningthe lightness and the flop index).

For this purpose, a laser beam is directed at an angle of 60° onto thesurface under investigation, and the instrument records the fluctuationsin the reflected light over a distance of 10 cm in the shortwave region(0.3 to 1.2 mm) and in the longwave region (1.2 to 12 mm) (longwave=LW;shortwave=SW; the lower the values, the better the appearance).Furthermore, as a measure of the sharpness of an image reflected in thesurface of the multilayer system, the instrument determines theparameter of “distinctness of image” (DOI) (the higher the value, thebetter the appearance).

These measurements are carried out before and after condensationexposure. For this purpose, the coated substrates are stored over aperiod of 10 days is a climate chamber under CH test conditionsaccording to DIN EN ISO 6270-2:2005-09 (date: September 2005). Thecoated substrates are subsequently inspected for swelling andblistering, 24 hours after removal from the climate chamber and theprofile and waviness are assessed.

The incidence of blisters is in this case assessed as follows by acombination of two values:

-   -   The number of blisters is evaluated by a quantity figure from 1        to 5, with ml denoting very few and m5 very many blisters.    -   The size of the blisters is evaluated by a size report, likewise        from 1 to 5, with g1 denoting very small and g5 very large        blisters.

The designation m0g0, accordingly, denotes a blister-free finish aftercondensation water storage, and represents satisfactory result in termsof blistering.

4.1.3 Determination of the Adhesion Properties

For determining the adhesion properties of the inventive coatingcompositions (or of comparative compositions), multicoat paint systemsare produced in accordance with the following general protocol:

Original Finish

Atop a metallic substrate coated with a cured electrocoat system(CathoGuard® 500 from BASF Coatings GmbH) with dimensions of 10×20 cm,the waterborne basecoat material is applied by means of dual appication;in the first step, application takes place electrostatically with atarget film thickness of 8-9 μm, and is the second step, after a2-minute flashing time at room temperature, pneumatically with a targetfilm thickness of 4-5 μm. The resulting waterborne basecoat film issubsequently dried, after a further flashing time of 5 minutes at roomtemperature, in a forced air oven at 80° C. for 5 minutes. Applied overthe dried waterborne basecoat film is a commercial two-componentclearcoat material (ProGloss from BASF Coatings GmbH), with a targetfilm thickness of 40-45 μm. The resulting clearcoat film is flashed atroom temperature for 10 minutes, followed by curing in a forced air ovenat 140° C. for 20 minutes more. The system obtainable in this way isreferred to below as original finish (system a).

Alternatively, curing of the basecoat and clearcoat films is carried outat 60 minutes/140° C. (referred to hereinafter as overbaked originalfinish; system c).

Refinishes

Over the original finish or alternatively over the overbaked originalfinishes, the waterborne basecoat material is again applied by dualapplication, with application in the first step taking placeelectrostatically (target film thickness of 8-9 μm) and in the secondstep, after a 2-minute flashing time at room temperature, pneumatically(target film thickness of 4-5 μm). The resulting waterborne basecoatfilm, after a further 5-minute flashing time at room temperature, issubsequently dried in a forced air oven at 80° C. for 10 minutes. Overthis dried waterborne basecoat film, a commercial two-componentclearcoat material (ProGloss from BASF Coatings GmbH) is applied, with atarget film thickness of 40-45 μm.

The resulting clearcoat film is flashed at room temperature for 10minutes; this is followed by curing in a forced air oven at 140° C. for20 minutes more. The system obtainable accordingly is referred to belowas refinish; depending on drying conditions of the original twodifferent multicoat systems result: system A is a refinish on system a;system C is a refinish on system c.

The technological properties of the multicoat systems were assessed byimplementing cross-cuts according to DIN EN ISO 2409 (rating GT 0 to GT5; 0 best score; 5=worst score). The corresponding investigations wereperformed on unexposed samples and also following expo sure tocondensation water. The condensation exposure, including subsequentassessment of the exposed samples for swelling and blistering, takesplace as described in section 4.1.2 (Assessment of appearance before andafter condensation exposure).

4.1.4 Determining the Initial Viscosity

The initial viscosity is determined after the basecoat materialcomponents have been weighed out in accordance with the preparationprotocols described below, but before the adjustment of the materials inquestion to a pH of 8 using dimethanolamine and also to a specifiedspray viscosity, by measuring the viscosity under a shear load of 1000s⁻¹ with a rotational viscometer (Rheolab QC instrument with C-LTD80/QCtemperature control system from Anton Paar) at 23° C.

4.1.6 Determining the Solids Content

The solids content of the basecoat materials is determined according toDIN EN ISO 3251, table A.1 (date: Jun. 1, 2008). Here, 1 g of sample areweighed out into an aluminum dish which has been dried before-hand, andthe sample is dried in a drying cabinet at 130° C. for 60 minutes,cooled in a desiccator, and then weighed again. The residue, based onthe total amount of the sample used, corresponds to the solids content.

4.2 Comparison Between the Inventive Waterborne Basecoat Material A3 andthe Noninventive Waterborne Basecoat Material A2 in Terms of Shade andAdhesion

Investigations on the waterborne basecoat materials A2 and also A3 takeplace in accordance with the methods described above. Tables 4.1 and 4.2summarize the results.

4.2.1 Comparison Between the Inventive Waterborne Basecoat Material A3and the Noninventive Waterborne Basecoat Material A2 in Terms of Shade

TABLE 4.1 Results in terms of shade A2 A3 L*_(15°) 118.2 124.3 L*_(25°)99.0 103.0 L*_(45°) 66.1 66.6 L*_(75°) 44.2 42.8 L*_(110°) 36.8 35.4Flop index 9.7 10.6

Using the inventive aqueous dispersion BM1 comprising theseed-core-shell acrylate SCS1 in the waterborne basecoat material A3leads, in comparison to the reference, the noninventive dispersion EM5comprising the multistage acrylate SCS5 in the waterborne basecoatmaterial A2, to an increase in the flop index, in other words to animprovement in the aluminum flake orientation.

4.2.2 Comparison Between the Inventive Waterborne Basecoat Material A3and the Noninventive Waterborne Basecoat Material A2 in Terms ofAdhesion Before and After Condensation Exposure

TABLE 4.2 Results for adhesion before and after condensation exposureClearcoat baking conditions in original system A2 A3 Adhesion oforiginal finish before/after condensation exposure System a beforecondensation GT0 GT0 exposure System a after condensation GT0 GT0exposure Refinish adhesion before condensation exposure A: standard(140° C./20 minutes) GT0 GT0 C: overbaked GT3 GT0 (140° C./60 minutes)Refinish adhesion after condensation exposure A: standard (140° C./20minutes) GT0 GT0 C: overbaked GT1 GT0 (140° C./60 minutes)

The inventive waterborne basecoat material A3 based on the aqueousdispersion BM1 comprising the seed-core-shell acrylate SCS1 exhibits noadhesion problems in any of the multicoat systems. Conversely, thenoninventive waterborne basecoat material A2 based on the noninventiveaqueous dispersion BMS comprising the multistage acrylate SCS5 exhibitspoorer adhesion, especially before condensation exposure, when theclearcoat of the original finish is overbaked at 140° C. for 60 minutes(system C) (plane of separation: refinish system on orginal system).

4.3 Comparison of Inventive Waterborne Basecoat Materials A4, A6 and A7with Noninventive Waterborne Basecoat Material A1

4.3.1 Comparison of Inventive Waterborne Basecoat Materials A4, A6 andA7 with Noninventive Waterborne Basecoat Material Al in Terms of Shade

A1 A4 A6 A7 L*_(15°) 125.5 134.7 127.1 128.6 L*_(25°) 102.27 105.1 103.8104.2 L*_(45°) 64.0 60.6 64.5 63.8 L*_(75°) 41.1 38.1 40.8 40.3L*_(110°) 34.2 32.5 34.0 33.9 Flop index 11.3 13.4 11.5 11.8

Using the inventive aqueous dispersions BM1, EM2, and BM3 in theinventive waterborne basecoat materials A4, A6, and A7 leads in allcases to improvement, in some cases significant, in the flop index incomparison to the noninventive waterborne basecoat material A1containing the noninventive aqueous dispersion BM5.

4.3.2 Comparison of Inventive Waterborne Basecoat Materials A4, A6 andA7 with Noninventive Waterborne Basecoat Material A1in Terms ofAppearance After Condensation Exposure

After condensation exposure A1 A4 A6 A7 LW: 2.3 2.8 1.8 2.6 SW: 18.5 9.39.9 13.9 DOI: 82.2 85.5 87.3 85.1 Swelling: cOK OK OK OK Blisteringm1/g1 m0/g0 m0/g0 m0/g0 OK = satisfactory cOK = conditionallysatisfactory m = number of blisters g = size of blisters

In terms of swelling and blistering after condensation exposure, thenoninventive waterborne basecoat material A1 containing the noninventivedispersion BM5 exhibits weaknesses, whereas the waterborne basecoatmaterials comprising the aqueous dispersions of the invention are allclassified as satisfactory.

Relative to the reference (waterborne basecoat material A1 based onBM5), the waterborne basecoat materials A4, A6 and A7 based on BM1, BM2and BM3 exhibit advantages in terms of shortwave (SW) and also DOI aftercondensation exposure.

1. An aqueous dispersion comprising at least one polymer, preparable by:i. polymerizing a mixture of olefinically unsaturated monomers A byemulsion polymerization in water, using at least one emulsifier and atleast one water-soluble initiator, wherein a polymer prepared from themonomers A has a glass transition temperature of 10 to 55° C., ii.polymerizing a mixture of olefinically unsaturated monomers B byemulsion polymerization in water, using at least one emulsifier and atleast one water-soluble initiator, in the presence of the polymerobtained under i., wherein a monomers concentration of 6.0 wt % in thereaction solution is not exceeded throughout the reaction period, andthe mixture of olefinically unsaturated monomers B comprises at leastone polyolefinically unsaturated monomer, iii. polymerizing a mixture ofolefinically unsaturated monomers C by emulsion polymerization in water,using at least one emulsifier and at least one water-soluble initiator,in the presence of the polymer obtained under ii., wherein a monomersconcentration of 6.0 wt % in the reaction solution is not exceededthroughout the reaction period, and iv. adjusting the pH of the reactionsolution to a pH of 6.5 to 9.0, wherein a. the mixture of olefinicallyunsaturated monomers A comprises from 0 wt % to less than 50.0 wt % ofone or more monomers having a solubility in water of <0.5 g/l at 25° C.,a monomers A concentration of 6.0 wt % in the reaction solution fromstage i. is not exceeded, and the resulting polymer after stage i. has aparticle size of 20 to 110 nm, b. a polymer prepared from the monomers Bhas a glass transition temperature of −35 to 12° C., and the resultingpolymer after stage ii. has a particle size of 130 to 200 nm, c. apolymer prepared from the monomers C has a glass transition temperatureof −50 to 15° C., and the resulting polymer after stage iii. has aparticle size of 150 to 280 nm.
 2. The aqueous dispersion of claim 1,wherein the mass of the monomer mixture A, based on the total mass ofthe monomer mixtures A, B and C, is 1 to 10%, the mass of the monomermixture B, based on the total mass of the monomer mixtures A, B and C,is 60 to 80%, and the mass of the monomer mixture C, based on the totalmass of the monomer mixtures A, B and C, is 10 to 30%.
 3. The aqueousdispersion of claim 1, wherein the emulsifiers used under i., ii., andiii. are selected, independently of one another, from the groupconsisting of ethoxylated and propoxylated alkanols having 10 to 40carbon atoms.
 4. The aqueous dispersion of claim 1, wherein the monomermixture A comprises at least one monounsaturated ester of (meth)acrylicacid having an unsubstituted alkyl radical and/or at least onevinylically monounsaturated monomer having an aromatic radical on thevinyl group.
 5. The aqueous dispersion of claim 1, wherein the monomermixture B comprises at least one polyolefinically unsaturated monomerand at least one monounsaturated ester of (meth)acrylic acid having anunsubstituted alkyl radical.
 6. The aqueous dispersion of claim 1,wherein the monomer mixture C comprises at least one alpha-betaunsaturated carboxylic acid, at least one monounsaturated ester of(meth)acrylic acid having an alkyl radical substituted by one or morehydroxyl groups and at least one monounsaturated ester of (meth)acrylicacid having an unsubstituted alkyl radical.
 7. A pigmented aqueousbasecoat material which comprises at least one aqueous dispersion ofclaim
 1. 8. The pigmented aqueous basecoat material of claim 7, whereinthe weight percentage fraction, based on the total weight of thepigmented aqueous basecoat material, of the at least one polymercomprised in the aqueous dispersion of any of claims 1 to 6 is 1.0 to24.0 wt %.
 9. The pigmented aqueous basecoat material of claim 7, whichcomprises as a binder at least one polyurethane resin.
 10. The pigmentedaqueous basecoat material of claim 7, which comprises a polyurethaneresin, said resin being grafted by means of olefinically unsaturatedmonomers and also containing hydroxyl groups, and also a melamine resin.11. A method of using an aqueous dispersion of claim 1, said methodcomprising using the aqueous dispersion in pigmented aqueous basecoatmaterials for improving adhesion.
 12. A process for producing amulticoat paint system, in which (1) a pigmented aqueous basecoatmaterial is applied to a substrate, (2) a polymer film is formed fromthe coating material applied in stage (1), (3) a clearcoat material isapplied to the resulting basecoat film, and subsequently (4) thebasecoat film is cured together with the clearcoat film, wherein apigmented aqueous basecoat material of claim 7 is used in stage (1). 13.The process of claim 12, wherein the substrate from stage (1) is amulticoat paint system which possesses defect sites.
 14. A multicoatpaint system producible by the process of claim
 12. 15. The process ofclaim 13, wherein the multicoat paint system employed as substrate andexhibiting defect sites is a system of claim 14.